1. Field of Invention
The present invention relates to a light transmission sheet, a mirror, a rear projection type projector, a light transmission sheet manufacturing device, a program, and a computer-readable medium that allow ghost images caused by retroreflection of projected light to be reduce or eliminated and high resolution images to be obtained.
2. Description of Related Art
A related art rear projection type projector includes a projector unit provided in a case, a mirror that reflects projected light emitted from the projector unit, and a transmission screen provided at the front of the case. The transmission screen is made of a combination of a Fresnel lens sheet and a lenticular lens sheet. The Fresnel lens sheet serves as a convex lens that curves projected light expanded as it is projected and widened outwardly by a projection lens toward the viewer side, so that the light is substantially perpendicular to the screen. The lenticular lens sheet controls the diffusion direction of the projected light.
The structure of the above-described rear projection type projector suffers from ghost images caused by retroreflection on the screen as its depth is reduced due to the arrangement. The rear projection type projector for home use in particular must have a small thickness so that it can be placed in any location as desired. Therefore, the transmission screen and the mirror are positioned to close to each other. This causes retroreflection between the plane of incidence of the transmission screen and the mirror, which is why ghost images are easily generated.
FIG. 9 is a schematic of the principle of how such a ghost image is generated by the retroreflection. Light L projected from the projector unit is reflected off a mirror 1 and enters a Fresnel lens sheet 2. Normal projected light Lc to be proper image light comes into a lenticular lens sheet 3 and is projected on the viewer side. Meanwhile, part of the projected light L coming into the plane 2a of the Fresnel lens sheet is reflected off this sheet plane. The reflected light Lr is reflected again off the mirror 1 to be retroreflection light, which enters the Fresnel lens sheet 2, and is projected through the lenticular lens sheet 3 to form a ghost image Lg.
Related art techniques of eliminating such ghost images are disclosed by Japanese Patent Laid-Open Nos. Hei 5-158153 and Hei 11-133508. A lens sheet as disclosed by Japanese Patent Laid-Open No. Hei 5-158153 is provided with irregularities on the surface, which does not form the Fresnel lens, of the lens sheet in order to reduce or eliminate the ghost images caused by the retroreflection. The irregularities reduce or prevent the retroreflection of the projected light, and reduce ghost images. The shape of the irregularities may be mat, hairline, and semicylindrical, such as a lenticular lens.
A transmission screen as disclosed by Japanese Patent Laid-Open No. Hei 11-133508 has a mat surface having a fine irregularities shape on the surface of a light diffusion sheet including fine particles and the surface is provided along with a Fresnel lens sheet. Retroreflection light is diffused by the mat surface to prevent ghost images from forming. The mat surface is formed by thermal transfer process with a metal die, blasting, hairline working, or the like.